The critical constituents in tobacco which maintain the habit and the rewarding psychological/physiological effects sought by the smoker are examined. The importance of nicotine in the smoking habit is assessed by using a device which allows subjects to control the nicotine content of smoke. In the first experiment, nicotine deprived subjects participate in two-hour sessions during which they smoke on the device that allows for nicotine mixing. A positive or negative accelerating curve across the puffs which fit the observed patterns is noted. In the second experiment, 30 smokers are seen for a total of five three-hour sessions. Each session consists of one of four procedures in which subjects smoke normally or preload with rapid smoking, slow smoking, or no consumption at all. The effects of smoking preload is then investigated with respect to physiological responses as well as to the motivation to smoke. By gaining a better understanding of why people smoke in specific circumstances, it may be possible to design more effective smoking-cessation strategies to help individuals avoid the health risks associated with smoking.